It's not a classic but I'm tidying up my GSX14 currently & this question could apply to bikes of any age.

I've stripped all the bits off/out of the tank & cleaned up some rust under the filler cap, but some water got inside the tank when I washing it. Because of the design I can't drain the last dregs out, I'd guess at about 1/3 of a mug in there. What's the best way to get it out chaps? or is that a small enough amount to just fill the tank & dilute it? It's a 22litre tank btw.

just drop in one of them microfibre cloths or even a jaycloth or bit of old toweling. once youve removed the bulk of it, a couple of hours sat in a sunny conservatory will dry it fully. if its already off, check that the little drain pipe from the filler cap recess is clear or else it will fill with rainwater which will drop into the tank every time you remove the filler.

well not neceessarily. any water wont be diluted by the fuel you put in. water will just sit at thee bottom of the tank under thee fueluntil it either gets dragged through the carbs or else it rusts away the inside of thee tank and lets itself out. unfortunately, with modern ethanol fuels, water vapour will be absorbed into the fuel from the air and then will condense out of solution as just water and collect in the tank. unfortunately, most bik fueel tanks dont have the fuel outlet at the absolute lowest point in the tank. so water that gets in ther will stay and not bee able to get out.